A safety restraint in the form of an inflatable cushion disposed within a supporting structure such as a dash panel, side door or other fixed portion of a car body in opposing relation to a seat in the vehicle plays an important role in protecting the occupants in a vehicle from injury due to collision against the car body. Typically, the inflatable cushion is inflated rapidly by the pressure of a reaction gas released from an inflator during a collision event. This gas generation typically takes place when a gas generating agent in the inflator induces a chemical reaction activated by a collision signal from a collision detecting sensor when the deceleration of the vehicle exceeds a certain level. The gas which is generated by the generator is then conveyed to the inflatable cushion which expands outwardly as it fills with gas to create a protective barrier between the vehicle occupant and the portion of the vehicle body against which the occupant might other wide be thrown.
Inflatable air bag systems have been used in the past to protect both the operator of the vehicle and passengers. Inflatable cushions for the protection of the vehicle operator have been mounted in the steering column of the vehicle and have utilized cushion constructions directly deployable towards the driver. These driver-side cushions are generally of a relatively simple configuration in that they function over a fairly small, well-defined area between the driver and the steering column. Inflatable cushions for use in the protection of passengers against frontal or side impacts must generally have a more complex configuration since the position of a vehicle passenger may not be well defined and greater distance may exists between the passenger and the surface of the vehicle against which that passenger might be thrown in the event of a collision. Curtain-type air bags that remain inflated for extended periods of time at positions between a vehicle occupant and windows or other points of possible ejection are also known for use in protecting occupants during an extended roll-over event.
Air bags of all constructions normally include one or more seams connecting panels of fabric together. In addition, curtain-type air bags often include an arrangement of welded or sewn seams inboard of the perimeter. These inboard seams form so called zero length tethers between opposing panels so as to define a desired arrangement of inflation zones while maintaining a substantially flat inflation profile.
Past air bag constructions have relied upon woven fabrics to provide multi-directional strength. While such woven constructions perform extremely well, such constructions also utilize substantial quantities of yarn and may be somewhat thick and bulky due to the fact that the yarns run over and under one another. It has also been proposed to use laminated weft inserted warp knit constructions in place of traditional woven constructions. By way of example only, prior air bag fabrics incorporating weft inserted warp knit constructions are disclosed in U.S. Pat. Nos. 5,916,830 and 5,945,359 to George M. Graham, the contents of all of which are hereby incorporated by reference as if fully set forth herein.
Regardless of the fabric construction utilized, the zones adjacent the seams may experience relatively high stress levels during inflation and impact as the panels held by the seams attempt to separate from one another. Due to these stress levels the zones immediately adjacent the seams may be subject to so called “combing” wherein the yarns adjacent the seam spread apart form one another under pressure and thereby cause increased gas leakage. In undesirable situations such combing may also be accompanied by localized yarn breakage due to stress and/or damage from sewing needles. In order to reduce adverse consequences of seam combing and yarn breakage it has been common practice to utilize tightly woven constructions wherein the yarns forming the fabric are packed together in interwoven relation at a relatively high density. Such constructions reduce combing and also tend to arrest any propagation of a tear if one develops in the fabric.
In the past, knit structures have generally been considered to have limited utility in an air bag environment due to the fact that such constructions may be more prone to combing due to reduced structural stability. Moreover, localized yarn breakage may lead to an unraveling of the fabric thereby leading to extended tears. In traditional weft inserted warp knit fabrics such as those described in U.S. Pat. Nos. 5,916,830 and 5,945,359 to George M. Graham, a layer of in-lay warp yarns is disposed across a layer of inserted weft yarns such that the warp yarns are disposed in a first plane and the weft yarns are in a second different plane. The warp yarns and the weft yarns are bound together by a smaller tying yarn or stitching yarn that is knit so as to form an arrangement of stitches with one stitch at each row. In these prior constructions if the tying yarn is broken such as when the fabric is cut or sewn, the tying yarn can begin to de-knit and the inlay warp yarns can pull away from the weft yarns. While the effect of such de-knitting may be at least partially addressed by using two or more layers of fabric laminated together, such lamination may give rise to an undue level of complexity. Moreover, the total thickness and fiber requirements for a multi-layer construction with two adjoined layers of weft inserted warp kit fabric may offer little improvement over traditional single layer woven constructions.